Resin compositions having high mechanical strength are required in a variety of fields. Therefore, the rigidity, heat resistance and impact resistance of resins have been improved by the dispersion of inorganic fillers as filling materials. In particular, many attempts at increasing the mechanical properties and heat resistance of macromolecular materials by means of the dispersion of fillers on the nano-level have been made.
For example, a method has been proposed of intercalating (inserting) a monomer which is a source for a macromolecular material between the layers of a layered clay mineral, then dispersing the layered clay mineral on the nano-level by applying energy when polymerizing the monomer (for example, see Japanese Patent Application, First Publication No. Hei2-102261 and Japanese Patent Application, First Publication No. Hei2-105856). Additionally, a method has been tested of pre-swelling a layered clay mineral with organic cations, then further performing unlimited swelling with an organic solvent so that the layered clay mineral takes the form of a cardhouse, then bringing this into contact with a polymer melt in order to disperse the layered clay minerals on the nano-level (Japanese Patent Application, First Publication No. Hei 7-70357).
However, of the above-mentioned methods, while the former which is due to polymerization efficiently disperses the filler, it requires equipment for polymerization, so that the production costs are high and cannot be considered to be economical. Additionally, at present, the reaction is restricted to condensation polymerization employed for polyamides, aromatic polyesters and the like, radical polymerization wherein reactive monomers such as heat-hardening types are entered between the layers, or cationic polymerization and the like.
Additionally, since the monomers inserted between the layers must stably exist within the layers, those which are gases at standard pressure are not suitable, so as to be restricted to liquid monomers.
Therefore, there is the drawback that only limited resin material and a low-concentration filler can be obtained when obtaining a resin composition dispersed with fillers on the angstrom-level.
As a result, it is not possible to use, for example, anionic coordination polymerization used for polyolefins. That is, if active hydrogens such as amino acids exist between the layers of the layered clay mineral, they act as a catalyst poison in titanium/organic aluminum anion coordination catalysis.
Additionally, with this method which is due to polymerization, the clay minerals react with amino groups when polyamide monomers are inserted between the layers, so that the terminal groups of the polyamides form carboxylic acids after polymerization. For this reason, the reactivity of the terminal groups is sealed off, and there is a marked reduction in the dye-affinity and adhesive property. Additionally, when forming a polymer alloy with other resins, there are problems in that the adhesive property at the interface is poor even if a compatibility agent has been added, as a result of which the dispersive phase tends to easily un-mix and the capabilities become difficult to activate. As a measure for improvement on this problem, a method has been proposed of adding polyhydric amines afterwards, in order to induce a reaction with the terminal groups of the polyamides (Japanese Patent Application, First Publication No. Sho 63-230766).
However, there are disadvantages in that it is difficult to induce a uniform reaction because a reaction cannot be performed in a dilute solvent, and in that intermolecular crosslinking is encouraged so that reductions in the fluidity and moldability are likely to occur. Similarly, in the case of polyesters, di-alcohols of the monomers become coordinated in the layered clay minerals, thus increasing the number of carboxylic acids at the terminals when performing macromolecularization. Therefore, when forming a polymer alloy with polycarbonates, ABS, PBT and the like, there are problems in that the adhesive property at the interface is poor even if a lot of compatibility agent is added, and consequently de-bonding tends to occur, thereby making the capabilities difficult to activate.
Additionally, the latter method of using an organic solvent requires the use of large quantities of solvent on the layered clay mineral, as described in the publication. Furthermore, the degree of dissolution in organic solvents can be extremely poor for some polymers, and there are those wherein a layered mineral on which unlimited swelling has been performed cannot form a solid solution in the polymer. These types have extremely low affinities with respect to the solvent even if the resin is melted. Consequently, even if a clay mineral with unlimited swelling which has been pre-formulated by an organic cationic treatment is brought into contact with the polymer in a melted state, it does not easily disperse or mix, and does not achieve complete dispersion.
Additionally, even if an interlayer compound obtained by bringing an organic cation into contact with a layered mineral is brought into a state of unlimited swelling by an organic solvent, there is a tendency to return from the state of unlimited swelling to the original swollen state because the organic solvent partially evaporates due to the heat in the extruder during the process of contact with the melted resin. For this reason, in actuality, the contact with the melted polymer occurs at a step wherein the interlayer distance is contracted, thus making it difficult to obtain a complete dispersion.
Here, if an amorphous resin is used as the resin and is combined with an organic solvent with a high affinity with respect to this resin, then the above-mentioned production process can achieve dispersion albeit incomplete, but it is extremely difficult to achieve good dispersion when a crystal material is used as the resin. For this reason, countermeasures have been taken by improving the extrusion apparatus so as to make the contact time longer by employing extruders wherein the ratio (LID) between the screw length (L) and the screw diameter (D) is 45 or more, and by using a batched kneader such as a banbury mixer, but the throughput by extrusion is markedly reduced due to the difficulty of removing the solvent, thus making these deficient in terms of their economical viability.